Rotary shock absorbers can be used between any angularly displaceable member and a stationary or supporting member and serve, as do linear shock absorbers, to damp vibration or other kinetic transmission between the two members.
For example, a rotary shock absorber can be used as part of a wheel suspension for a vehicle, especially a track vehicle whose ground-engaging member, e.g. the track, is supported by, guided along or passes around a wheel which is yieldably mounted with respect to the vehicle body or chassis, e.g. on an arm.
The track-supporting arms generally connected to the vehicle chassis or body through the intermediary of rotary shock absorbers, e.g. shock absorbers capable of damping shock or vibration transmission from an angularly displaceable member to a nondisplaceable member.
Conventional rotary shock absorbers (see German open application DE-OS No. 2,457,042) comprise a rotor member which can be connected to the angularly displaceable element and a stator member which can be connected to a relatively stationary element, e.g. a vehicle chassis, and a viscous liquid filling a space defined between these elements and within which vanes may move.
The ends of the vanes may define throttling gaps with the chamber walls so that the rotor in effect forms an inefficient vane-type pump in which relative angular displacement of the rotor and stator is converted to forced displacement of the viscous liquid through throttling gaps and hence into thermal energy.
This bulk displacement principle of shock damping has the disadvantage that the damping effect is dependent in large measure upon critical tolerances of the gap width or flow cross section which cannot be maintained in use and are difficult to establish upon fabrication.
Another disadvantage of this earlier shock absorber construction is that the angular displacement of the rotor is also limited and hence the shock absorber has little versatility and, more specifically, is not amenable to many applications in which a considerable angular stroke is desired between the rotor and the stator.
In another rotary shock absorber (see British Pat. No. 1,484,938) an annular disc is mounted upon a shaft and defines shear gaps with the housing closely surrounding this disc.
A shear gap is a space filled with a liquid, the space being generally sufficiently narrow so that friction between the liquid and the surfaces of the disc and the housing retains certain thicknesses of the liquid against these surfaces so that shear forces are established within the body of liquid, i.e. between the films frictionally adherent to the surfaces and the body of liquid.
The damper of the British patent appears to have utility primarily for weapons systems in which substantial amplitudes of angular displacement are required and must be damped as the weapons system is brought to bear upon a target. Efforts to apply such dampers to vehicle applications and especially to the suspension of track vehicles have proved to be unsuccessful. Apparently, the problem in such application is that the angular velocity in vehicle applications can range from extremely high velocities to extremely low velocities and the shear resistance with extremely low velocities increases markedly and falls sharply with increasing velocities. As a result, the damping effect varies inappropriately.
I have also found that the system of the British patent has the additional disadvantage that it is highly sensitive to tolerances of the type mentioned previously because the maintenance of the narrow shear gap is critical.